Electric arc spray guns are well known in the art, for example as disclosed in U.S. Pat. No. 4,668,852. The ends of two electrically isolated metal wires are melted in an electric arc struck between the wire ends. The molten metal is atomized by compressed gas, usually air, and sprayed to a workpiece to be coated. Such guns are usually utilized for spraying on open surfaces and, in part because of the need to accommodate the spray wires feeding into the gun, are not generally suitable for spraying into confined areas, particularly on the sides of deep holes. One approach is to position a spray head at an angle to coat such areas, but the spray wires cannot bend enough for spraying in the preferred direction normal to the surface. Thus, in order to spray coatings in such areas, it sometimes becomes necessary to deflect the spray stream.
The aforementioned patent includes disclosure of particular gas caps that may be fitted on a head member containing pressure contact means and wire guides for the wires, the head member also containing a gas jet nozzle for the atomization and spraying. With one such gas cap it is disclosed that a secondary gas is directed to modify the spray stream, for example to deflect the same. No details are provided for optimization of such deflection or the coatings produced thereby.
British Patent Specification No. 1,346,054 teaches that the atomizing nozzle may be positioned to obliquely direct air to the wire tips for spraying the interior of a tube. However, it has been found that such a single jet system does not provide sufficient control to produce coatings of suitable quality.
U.S. Pat. No. 4,464,414 similarly discloses an oblique side jet of air in conjunction with an air stream directed along wires being melted, and a "blowing-away stream" for clearing dust from the coating area. Again, details are not provided for optimizing coatings, especially for different types of wires.